Alpha9 and beta8 integrin expression correlates with the merger of the developing mouse eyelids.
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As previously reported, alpha9 integrin is expressed between the merged or fused eyelids of mice at birth, and changes in alpha9 localization occur during lid opening. To determine whether alpha9 and/or additional integrin subunits mediate the emergence and temporary fusion of the eyelids, immunofluorescence and confocal microscopy were used to evaluate the localization of various integrin subunits in the developing ocular surface of the mouse. No detectable beta5, beta6, or beta7 integrins were observed on the epithelia of the ocular surface. alpha2, alpha3, alphav, and beta1 integrins were most abundant in the basal cells beginning at 13.5 days post conception and remained primarily localized to the basal cell layers throughout development. beta4 was localized at the basal surface of the epidermal basal cells beginning at 13.5 days post conception but was not found on the corneal epithelial basal cells until after birth. alpha9 and beta8 integrins were present on suprabasal cells of the epidermis at the leading edge of the eyelid before merger and on the epithelial bridge that forms immediately after these tissues merge, suggesting that they play a role in the initial fusion of the epithelial tissues of the eyelid and in stabilizing the epithelial junction. After birth and into adulthood, beta8 was retained within the suprabasal cell layers of the epidermis, whereas alpha9 became localized to the basal cells of the epidermis, the conjunctiva, and the limbus. The lack of co-localization of beta4 with either alpha9 or beta8 in double-labeling studies suggests that alpha9 and beta8 are restricted to the lateral and apical aspects of those cells in which they are expressed. The presence of tenascin-C and laminin-5 at the epithelial junction site suggests that alpha9: tenascin-C and beta4: laminin-5 interactions may play a role in stabilizing the fusion between lids early on but do not appear to be involved in the movement of the lids across the cornea. The data presented identify specific integrins and matrix proteins that are likely to mediate eyelid fusion. (+info)
Uncoupling integrin adhesion and signaling: the betaPS cytoplasmic domain is sufficient to regulate gene expression in the Drosophila embryo.
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Integrin cell surface receptors are ideally suited to coordinate cellular differentiation and tissue assembly during embryogenesis, as they can mediate both signaling and adhesion. We show that integrins regulate gene expression in the intact developing embryo by identifying two genes that require integrin function for their normal expression in Drosophila midgut endodermal cells. We determined the relative roles of integrin adhesion versus signaling in the regulation of these integrin target genes. We find that integrin-mediated adhesion is not required between the endodermal cells and the surrounding visceral mesoderm for integrin target gene expression. In addition, a chimeric protein that lacks integrin-adhesive function, but maintains the ability to signal, can substitute for the endogenous integrin and regulate integrin target genes. This chimera consists of an oligomeric extracellular domain fused to the integrin betaPS subunit cytoplasmic domain; a control monomeric extracellular domain fusion does not alter integrin target gene expression. Therefore, oligomerization of the 47-amino-acid betaPS intracellular domain is sufficient to initiate a signaling pathway that regulates gene expression in the developing embryo. (+info)
The integrin alpha9beta1 mediates adhesion to activated endothelial cells and transendothelial neutrophil migration through interaction with vascular cell adhesion molecule-1.
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The integrin alpha9beta1 has been shown to be widely expressed on smooth muscle and epithelial cells, and to mediate adhesion to the extracellular matrix proteins osteopontin and tenascin-C. We have found that the peptide sequence this integrin recognizes in tenascin-C is highly homologous to the sequence recognized by the closely related integrin alpha4beta1, in the inducible endothelial ligand, vascular cell adhesion mole-cule-1 (VCAM-1). We therefore sought to determine whether alpha9beta1 also recognizes VCAM-1, and whether any such interaction would be biologically significant. In this report, we demonstrate that alpha9beta1 mediates stable cell adhesion to recombinant VCAM-1 and to VCAM-1 induced on human umbilical vein endothelial cells by tumor necrosis factor-alpha. Furthermore, we show that alpha9beta1 is highly and selectively expressed on neutrophils and is critical for neutrophil migration on VCAM-1 and tenascin-C. Finally, alpha9beta1 and alpha4 integrins contribute to neutrophil chemotaxis across activated endothelial monolayers. These observations suggest a possible role for alpha9beta1/VCAM-1 interactions in extravasation of neutrophils at sites of acute inflammation. (+info)
Intraepithelial lymphocytes traffic to the intestine and enhance resistance to Toxoplasma gondii oral infection.
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Toxoplasma gondii Ag-primed intraepithelial lymphocytes (IEL) from the mouse intestine have been shown to be protective against an lethal parasite challenge when adoptively transferred into recipient mice. In the present study, we observed that Ag-primed IEL traffic to the intestine of naive mice following i.v. administration. Primed and CD8beta+ IEL were the most efficient cells at homing to the host organ. In congenic mice, IEL migrated from intestine within several hours posttransfer. On Ag reexposure, the primed IEL return to the intestine where they enhance resistance as determined by reduction in the number of brain cysts. Treatment of recipient mice with anti-alpha4 and anti-alphaE Abs partially inhibited IEL intestinal homing. The Ab treatment dramatically impaired resistance to a subsequent oral infection. These finding indicate that lymphocyte homing is an important parameter in establishing long term immunity to recurrent infection with this parasite. (+info)
Mucosal T lymphocyte numbers are selectively reduced in integrin alpha E (CD103)-deficient mice.
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The mucosal lymphocyte integrin alpha E(CD103)beta 7 is thought to be important for intraepithelial lymphocyte (IEL) localization or function. We cloned the murine integrin gene encoding alpha E, localized it to chromosome 11, and generated integrin alpha E-deficient mice. In alpha E-/- mice, intestinal and vaginal IEL numbers were reduced, consistent with the known binding of alpha E beta 7 to E-cadherin expressed on epithelial cells. However, it was surprising that lamina propria T lymphocyte numbers were diminished, as E-cadherin is not expressed in the lamina propria. In contrast, peribronchial, intrapulmonary, Peyer's patch, and splenic T lymphocyte numbers were not reduced in alpha E-deficient mice. Thus, alpha E beta 7 was important for generating or maintaining the gut and vaginal T lymphocytes located diffusely within the epithelium or lamina propria but not for generating the gut-associated organized lymphoid tissues. Finally, the impact of alpha E deficiency upon intestinal IEL numbers was greater at 3-4 wk of life than in younger animals, and affected the TCR alpha beta+ CD8+ T cells more than the gamma delta T cells or the TCR alpha beta+ CD4+CD8- population. These findings suggest that alpha E beta 7 is involved in the expansion/recruitment of TCR alpha beta+ CD8+ IEL following microbial colonization. Integrin alpha E-deficient mice will provide an important tool for studying the role of alpha E beta 7 and of alpha E beta 7-expressing mucosal T lymphocytes in vivo. (+info)
Muscle LIM proteins are associated with muscle sarcomeres and require dMEF2 for their expression during Drosophila myogenesis.
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A genetic hierarchy of interactions, involving myogenic regulatory factors of the MyoD and myocyte enhancer-binding 2 (MEF2) families, serves to elaborate and maintain the differentiated muscle phenotype through transcriptional regulation of muscle-specific target genes. Much work suggests that members of the cysteine-rich protein (CRP) family of LIM domain proteins also play a role in muscle differentiation; however, the specific functions of CRPs in this process remain undefined. Previously, we characterized two members of the Drosophila CRP family, the muscle LIM proteins Mlp60A and Mlp84B, which show restricted expression in differentiating muscle lineages. To extend our analysis of Drosophila Mlps, we characterized the expression of Mlps in mutant backgrounds that disrupt specific aspects of muscle development. We show a genetic requirement for the transcription factor dMEF2 in regulating Mlp expression and an ability of dMEF2 to bind, in vitro, to consensus MEF2 sites derived from those present in Mlp genomic sequences. These data suggest that the Mlp genes may be direct targets of dMEF2 within the genetic hierarchy controlling muscle differentiation. Mutations that disrupt myoblast fusion fail to affect Mlp expression. In later stages of myogenic differentiation, which are dedicated primarily to assembly of the contractile apparatus, we analyzed the subcellular distribution of Mlp84B in detail. Immunofluorescent studies revealed the localization of Mlp84B to muscle attachment sites and the periphery of Z-bands of striated muscle. Analysis of mutations that affect expression of integrins and alpha-actinin, key components of these structures, also failed to perturb Mlp84B distribution. In conclusion, we have used molecular epistasis analysis to position Mlp function downstream of events involving mesoderm specification and patterning and concomitant with terminal muscle differentiation. Furthermore, our results are consistent with a structural role for Mlps as components of muscle cytoarchitecture. (+info)
The leukocyte integrin alpha D beta 2 binds VCAM-1: evidence for a binding interface between I domain and VCAM-1.
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The trafficking of leukocytes through tissues is supported by an interaction between the beta 2 (CD18) integrins CD11a/CD18 (LFA-1) and CD11b/CD18 (Mac-1) and their ligand ICAM-1. The most recently identified and fourth member of the beta 2 integrins, alpha D beta 2, selectively binds ICAM-3 and does not appear to bind ICAM-1. We have reported recently that alpha D beta 2 can support eosinophil adhesion to VCAM-1. Here we demonstrate that expression of alpha D beta 2 in a lymphoid cell that does not express alpha 4 integrins confers efficient binding to VCAM-1. In addition, a soluble form of alpha D beta 2 binds VCAM-1 with greater efficiency relative to ICAM-3. The I domain of alpha D contains a binding site for VCAM-1 since recombinant alpha D I domain binds specifically to VCAM-1. In addition, alpha D mAb that block cellular binding to VCAM-1 bind the alpha D I domain. Using VCAM-1 mutants we have determined that the binding site on VCAM-1 for alpha D beta 2 overlaps with that of alpha 4++ integrins. Substitution of VCAM-1 aspartate at position 40, D40, within the conserved integrin binding site, diminishes binding to alpha D beta 2 and abrogates binding to the alpha D I domain. The corresponding integrin binding site residue in ICAM-3 is also essential to alpha D beta 2 binding. Finally, we demonstrate that alpha D beta 2 can support lymphoid cell adhesion to VCAM-1 under flow conditions at levels equivalent to those mediated by alpha 4 beta 1. These results indicate that VCAM-1 can bind to an I domain and that the binding of alpha D beta 2 to VCAM-1 may contribute to the trafficking of a subpopulation of leukocytes that express alpha D beta 2. (+info)
cDNA cloning and chromosomal localization of human alpha(11) integrin. A collagen-binding, I domain-containing, beta(1)-associated integrin alpha-chain present in muscle tissues.
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We previously identified a novel integrin alpha-chain in human fetal muscle cells (Gullberg, D., Velling, T., Sjoberg, G., and Sejersen, T. (1995) Dev. Dyn. 204, 57-65). We have now isolated the full-length cDNA for this integrin subunit, alpha(11). The open reading frame of the cDNA encodes a precursor of 1188 amino acids. The predicted mature protein of 1166 amino acids contains seven conserved FG-GAP repeats, an I domain with a metal ion-dependent adhesion site motif, a short transmembrane region, and a unique cytoplasmic domain of 24 amino acids containing the sequence GFFRS. alpha(11), like other I domain integrins, lacks a dibasic cleavage site for generation of a heavy chain and a light chain, and it contains three potential divalent cation binding sites in repeats 5-7. The presence of 22 inserted amino acids in the extracellular stalk portion (amino acids 804-826) distinguishes the alpha(11) integrin sequence from other integrin alpha-chains. Amino acid sequence comparisons reveal the highest identity of 42% with the alpha(10) integrin chain. Immunoprecipitation with antibodies to alpha(11) integrin captures a 145-kDa protein distinctly larger than the 140-kDa alpha(2) integrin chain when analyzed by SDS-polyacrylamide gel electrophoresis under nonreducing conditions. Fluorescence in situ hybridization maps the integrin alpha(11) gene to chromosome 15q23, in the vicinity of an identified locus for Bardet-Biedl syndrome. Based on Northern blotting, integrin alpha(11) mRNA levels are high in the adult human uterus and in the heart and intermediate in skeletal muscle and some other tissues tested. During in vitro myogenic differentiation, alpha(11) mRNA and protein are up-regulated. Studies of ligand binding properties show that alpha(11)beta(1) binds collagen type I-Sepharose, and cultured muscle cells localize alpha(11)beta(1) into focal contacts on collagen type I. Future studies will reveal the importance of alpha(11)beta(1) for muscle development and integrity in adult muscle and other tissues. (+info)